Fibrous structures comprising non-naturally occurring hardwood pulp fibers

ABSTRACT

Fibrous structures employing non-naturally occurring hardwood pulp fibers, and more particularly, sanitary tissue products employing non-naturally occurring hardwood pulp fibers and methods for making same are provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/252,394 filed Oct. 16, 2009.

FIELD OF THE INVENTION

The present invention relates to fibrous structures comprising non-naturally occurring hardwood pulp fibers, and more particularly, sanitary tissue products comprising non-naturally occurring hardwood pulp fibers and methods for making same.

BACKGROUND OF THE INVENTION

Fibrous structures and/or sanitary tissue products comprising hardwood pulp fibers including non-naturally occurring hardwood pulp fibers are known in the art. However, the level of hardwood pulp fibers that formulators have used in their fibrous structures and/or sanitary tissue products have been limited due to the fact that hardwood pulp fibers conventionally have not exhibited the tensile strengths desired by consumers of such fibrous structures and/or sanitary tissue products. Therefore, formulators have had to use a mixture of hardwood pulp fibers and softwood pulp fibers to achieve the tensile strengths needed in their fibrous structures and/or sanitary tissue products.

Due to the costs differences between softwood pulp fibers and hardwood pulp fibers (softwood pulp fibers typically being more expensive) formulators desire to increase the hardwood pulp fiber levels and decrease the softwood pulp fiber levels in their fibrous structures and/or sanitary tissue products. Formulators have not had success in doing so due to the tensile strength differences between softwood pulp fibers and conventional hardwood pulp fibers and the drainage properties (as represented by PFR) of conventional hardwood pulp fibers.

It is known that hardwoods increase the softness of the fibrous structures in which they are present. Therefore, there is a continuing desire, especially for softer fibrous structures, to increase the level of hardwood present in fibrous structures.

Accordingly, there is a need for fibrous structures and/or sanitary tissue products comprising hardwood pulp fibers that overcome or at least partially overcome the differences between softwood pulp fibers and conventional hardwood pulp fibers and/or that overcome the negatives associated with conventional hardwood pulp fibers.

SUMMARY OF THE INVENTION

The present invention fulfills the need described above by providing fibrous structures and/or sanitary tissue products comprising hardwood pulp fibers that overcome or at least partially overcome the differences between softwood pulp fibers and conventional hardwood pulp fibers and/or that overcome the negatives associated with conventional hardwood pulp fibers.

In one example of the present invention, a fibrous structure comprising a non-naturally occurring hardwood pulp fiber that exhibits a handsheet tensile strength as measured according to the Handsheet Tensile Strength Test Method described herein less than the handsheet tensile strength of the non-naturally occurring hardwood pulp fiber in its naturally occurring state, is provided.

In another example of the present invention, a sanitary tissue product comprising a non-naturally occurring hardwood pulp fiber that exhibits a handsheet tensile strength as measured according to the Handsheet Tensile Strength Test Method described herein less than the handsheet tensile strength of the non-naturally occurring hardwood pulp fiber in its naturally occurring state, wherein the sanitary tissue product exhibits a greater wet burst strength as measured according to the Wet Burst Strength Test Method described herein and/or a greater initial total wet tensile as measured by the Initial Total Wet Tensile Test Method described herein than a sanitary tissue product that comprises the non-naturally occurring hardwood pulp fiber in its naturally occurring state, is provided.

In yet another example of the present invention, a fibrous structure comprising an enzyme treated hardwood pulp fiber that exhibits a handsheet tensile strength as measured according to the Handsheet Tensile Strength Test Method described herein less than the handsheet tensile strength of the hardwood pulp fiber without the enzyme treatment, is provided.

In still another example of the present invention, a sanitary tissue product comprising an enzyme treated hardwood pulp fiber that exhibits a handsheet tensile strength as measured according to the Handsheet Tensile Strength Test Method described herein less than the handsheet tensile strength of the non-enzyme treated hardwood pulp fiber, wherein the sanitary tissue product exhibits a greater wet burst strength as measured according to the Wet Burst Strength Test Method described herein and/or a greater initial total wet tensile as measured by the Initial Total Wet Tensile Test Method described herein than a sanitary tissue product that comprises the non-enzyme treated hardwood pulp fiber, is provided.

In even yet another example of the present invention, a method for making a fibrous structure comprising the steps of:

-   -   a. providing a fibrous composition comprising a non-naturally         occurring hardwood pulp fiber that exhibits a handsheet tensile         strength as measured according to the Handsheet Tensile Strength         Test Method described herein less than the handsheet tensile         strength of the non-naturally occurring hardwood pulp fiber in         its naturally occurring state; and     -   b. depositing the fibrous composition onto a collection device,         such as a fabric and/or a belt, to form a fibrous structure.

Accordingly, the present invention provides fibrous structures and/or sanitary tissue products comprising novel non-naturally occurring hardwood pulp fibers and method for making such fibrous structures and/or sanitary tissue products.

DETAILED DESCRIPTION OF THE INVENTION Definitions

“Pulp fiber” as used herein means a virgin fiber obtained from a tree or plant.

A specific type of pulp fiber is a wood fiber. “Wood fiber” as used herein means a virgin fiber obtained from a tree.

Pulp (one or more pulp fibers) may be chemical pulps, such as kraft (sulfate) and sulfite pulps, as well as mechanical and semi-chemical pulps including, for example, groundwood, thermomechanical pulp, chemi-mechanical pulp (CMP), chemi-thermomechanical pulp (CTMP), neutral semi-chemical sulfite pulp (NSCS).

The pulp fibers may be short (typical of hardwood fibers) or long (typical of softwood fibers).

“Hardwood pulp fiber” as used herein means pulp fibers obtained from deciduous trees. Non-limiting examples of deciduous trees include Northern hardwood trees and tropical hardwood trees. Non-limiting examples of hardwood pulp fibers include hardwood pulp fibers obtained from a fiber source selected from the group consisting of Acacia, Eucalyptus, Maple, Oak, Aspen, Birch, Cottonwood, Alder, Ash, Cherry, Elm, Hickory, Poplar, Gum, Walnut, Locust, Sycamore, Beech, Catalpa, Sassafras, Gmelina, Albizia, Anthocephalus, Magnolia, and mixtures thereof. In one example, the hardwood pulp fiber of the present invention is obtained from Eucalyptus.

“Tropical hardwood pulp fiber” as used herein means pulp fibers obtained from a tropical hardwood tree. Non-limiting examples of tropical hardwood trees include Eucalyptus trees and/or Acacia trees.

“Naturally occurring hardwood pulp fiber” as used herein means a pulp fiber that is found in nature or that has only been subjected to conventional pulping and/or bleaching processes without the presence of enzymes.

“Non-naturally occurring hardwood pulp fiber” as used herein means a naturally occurring hardwood pulp fiber that has been modified and/or treated by humans through a human-designed process and/or a human executed modifying and/or treating process. A naturally occurring hardwood pulp fiber that has been treated with an enzyme, such as during the pulping process, is a non-naturally occurring hardwood pulp fiber. In one example, a non-naturally occurring hardwood pulp fiber is a Eucalyptus pulp fiber that has been treated with an enzyme composition, for example an enzyme composition comprising xylanase.

“Fibrous structure” as used herein means a structure that comprises one or more pulp fibers. Non-limiting examples of processes for making fibrous structures include known wet-laid papermaking processes and air-laid papermaking processes. Such processes typically include steps of preparing a pulp fiber composition, oftentimes referred to as a fiber slurry in wet-laid processes, either wet or dry, and then depositing a plurality of fibers onto a forming wire or belt such that an embryonic fibrous structure is formed, drying and/or bonding the fibers together such that a fibrous structure is formed, and/or further processing the fibrous structure such that a finished fibrous structure is formed. For example, in typical papermaking processes, the finished fibrous structure is the fibrous structure that is wound on the reel at the end of papermaking, but before converting thereof into a sanitary tissue product.

Non-limiting types of fibrous structures according to the present invention include conventionally felt-pressed fibrous structures; pattern densified fibrous structures; and high-bulk, uncompacted fibrous structures. The fibrous structures may be of a homogeneous or multilayered (two or three or more layers) construction; and the sanitary tissue products made therefrom may be of a single-ply or multi-ply construction.

The fibrous structures may be post-processed, such as by embossing and/or calendaring and/or folding and/or printing images thereon.

The fibrous structures may be through-air-dried fibrous structures or conventionally dried fibrous structures.

The fibrous structures may be creped or uncreped.

The fibrous structures of the present invention may comprise, in addition to non-naturally occurring hardwood pulp fibers, naturally occurring pulp fibers, such as naturally occurring hardwood pulp fibers, naturally occurring softwood pulp fibers, synthetic fibers and/or filaments, such as polypropylene filaments, naturally occurring animal fibers, other naturally occurring plant fibers, and other non-naturally occurring fibers. The fibers may be in different layers within the fibrous structure or may be blended together in a single layer.

“Sanitary tissue product” comprises one or more fibrous structures, converted or not, that is useful as a wiping implement for post-urinary and post-bowel movement cleaning (toilet paper), for otorhinolaryngological discharges (facial tissue and/or disposable handkerchiefs), and multi-functional absorbent and cleaning uses (absorbent towels and/or wipes). The sanitary tissue product may be convolutedly wound upon itself about a core or without a core to form a sanitary tissue product roll.

In one example, the sanitary tissue product of the present invention comprises one or more fibrous structures according to the present invention.

The sanitary tissue products of the present invention may exhibit a basis weight between about 10 g/m² to about 120 g/m² and/or from about 15 g/m² to about 110 g/m² and/or from about 20 g/m² to about 100 g/m² and/or from about 30 to 90 g/m². In addition, the sanitary tissue product of the present invention may exhibit a basis weight between about 40 g/m² to about 120 g/m² and/or from about 50 g/m² to about 110 g/m² and/or from about 55 g/m² to about 105 g/m² and/or from about 60 to 100 g/m².

The sanitary tissue products of the present invention may be in the form of sanitary tissue product rolls. Such sanitary tissue product rolls may comprise a plurality of connected, but perforated sheets of fibrous structure, that are separably dispensable from adjacent sheets.

The sanitary tissue products of the present invention may comprises additives such as softening agents, temporary wet strength agents, permanent wet strength agents, bulk softening agents, lotions, silicones, wetting agents, latexes, patterned latexes and other types of additives suitable for inclusion in and/or on sanitary tissue products.

“Ply” or “Plies” as used herein means an individual finished fibrous structure optionally to be disposed in a substantially contiguous, face-to-face relationship with other plies, forming a multiple ply finished fibrous structure product and/or sanitary tissue product. It is also contemplated that a single fibrous structure can effectively form two “plies” or multiple “plies”, for example, by being folded on itself.

“Wet burst strength” as used herein is a measure of the ability of a fibrous structure and/or a sanitary tissue product incorporating a fibrous structure to absorb energy, when wet and subjected to deformation normal to the plane of the fibrous structure and/or fibrous structure product.

Non-naturally Occurring Hardwood Pulp Fibers

The non-naturally occurring hardwood pulp fibers of the present invention exhibit a handsheet tensile strength as measured according to the Handsheet Tensile Strength Test Method described herein less than the handsheet tensile strength of the non-naturally occurring hardwood pulp fiber in its naturally occurring state.

Further, the non-naturally occurring hardwood pulp fibers of the present invention exhibit the lower handsheet tensile strength without increasing the PFR of the hardwood pulp fibers as measured in their naturally occurring state. As a result, the non-naturally occurring hardwood pulp fibers provide a weaker fiber with respect to its handsheet tensile strength that dries and/or drains as good or better, as measured according to the PFR Test Method described herein, than the same hardwood pulp fibers as measured in their naturally occurring state.

Unexpectedly, the non-naturally occurring hardwood pulp fibers of the present invention, which weaker than their naturally occurring state, result in a sanitary tissue product comprising such non-naturally occurring hardwood pulp fibers exhibiting a greater wet burst strength and/or initial total wet tensile than a sanitary tissue product comprising the non-naturally occurring hardwood pulp fibers in their naturally occurring state.

Table 1 below evidences the differences between the fibrous structures and/or sanitary tissue products (A-C) comprising the non-naturally occurring hardwood pulp fibers of the present invention compared to a fibrous structure and/or sanitary tissue product (Control) comprising the hardwood pulp fibers in their naturally occurring state. The non-naturally occurring hardwood pulp fibers used in A and B were treated with a xylanase. The non-naturally occurring hardwood pulp fibers used in C were treated with an enzyme composition comprising xylanase and cellulase.

TABLE 1 Property Control A B C Handsheet Tensile Strength 428 353 290 401 (g/in per lb/3,000 ft²) PFR (s²) 7.4 7.1 6.9 7.4 Sanitary Tissue Product Wet 418 465 Did not 464 Burst Strength (g) measure Sanitary Tissue Product 56.6 62.6 68.4 65.8 Initial Total Wet Tensile (g/in) Relative Softness compared — Softer Softer Less soft to Control

The non-naturally occurring hardwood pulp fibers for use in the fibrous structures and/or sanitary tissue products of the present invention may exhibit a PFR of 7.4 or less and/or less than 7.3 and/or less than 7.2 and/or less than 7.1 and/or less than 7.0 to about 0 and/or to about 1 and/or to about 2 as measured according to the PFR Test Method described herein.

Enzymes

In one example of the present invention, the non-naturally occurring hardwood pulp fibers of the present invention may be derived from enzymatically treating naturally occurring hardwood pulp fibers. The enzyme and/or enzyme composition useful in enzymatically treating the naturally occurring hardwood pulp fibers comprises a xylanase enzyme.

In one example, the enzyme composition used to enzymatically treat the naturally occurring hardwood pulp fibers comprises xylanase and cellulase.

Fibrous Structure

The fibrous structure of the present invention comprises one or more non-naturally occurring hardwood pulp fibers that exhibit a handsheet tensile strength less than the handsheet tensile strength of the non-naturally occurring hardwood pulp fiber in its naturally occurring state as measured according to the Handsheet Tensile Strength Test Method described herein. In one example, the fibrous structure comprises at least 5% and/or at least 10% and/or at least 20% and/or at least 30% and/or at least 40% to about 100% and/or to about 90% and/or to about 80% and/or to about 70% and/or to about 60% by weight on a dry fiber basis of non-naturally occurring hardwood pulp fibers that exhibit a handsheet tensile strength less than the handsheet tensile strength of the non-naturally occurring hardwood pulp fiber in its naturally occurring state as measured according to the Handsheet Tensile Strength Test Method described herein.

In addition to the non-naturally occurring hardwood pulp fibers, the fibrous structures of the present invention may comprise softwood pulp fibers, such as Northern Softwood Kraft pulp fibers (NSK). In one example, the fibrous structure comprises from about 0 to about 90% and/or from about 10 to about 80% and/or from about 30 to about 70% by weight on a dry fiber basis of softwood pulp fibers and from about 10 to about 100% and/or from about 20 to about 90% and/or from about 30 to about 70% by weight on a dry fiber basis of hardwood pulp fibers at least a portion of which comprises non-naturally occurring hardwood pulp fibers that exhibit a handsheet tensile strength less than the handsheet tensile strength of the non-naturally occurring hardwood pulp fiber in its naturally occurring state as measured according to the Handsheet Tensile Strength Test Method described herein.

In another example, the fibrous structure of the present invention comprises one or more enzyme treated hardwood pulp fibers that exhibit a handsheet tensile strength less than the handsheet tensile strength of the non-enzyme treated hardwood pulp fiber as measured according to the Handsheet Tensile Strength Test Method described herein. In one example, the fibrous structure comprises at least 5% and/or at least 10% and/or at least 20% and/or at least 30% and/or at least 40% to about 100% and/or to about 90% and/or to about 80% and/or to about 70% and/or to about 60% by weight on a dry fiber basis of enzyme treated hardwood pulp fibers that exhibit a handsheet tensile strength less than the handsheet tensile strength of the non-enzyme treated hardwood pulp fiber as measured according to the Handsheet Tensile Strength Test Method described herein.

In addition to the enzyme treated hardwood pulp fibers, the fibrous structures of the present invention may comprise softwood pulp fibers, such as Northern Softwood Kraft pulp fibers (NSK). In one example, the fibrous structure comprises from about 0 to about 90% and/or from about 10 to about 80% and/or from about 30 to about 70% by weight on a dry fiber basis of softwood pulp fibers and from about 10 to about 100% and/or from about 20 to about 90% and/or from about 30 to about 70% by weight on a dry fiber basis of hardwood pulp fibers at least a portion of which comprises enzyme treated hardwood pulp fibers that exhibit a handsheet tensile strength less than the handsheet tensile strength of the non-enzyme treated hardwood pulp fiber as measured according to the Handsheet Tensile Strength Test Method described herein.

Sanitary Tissue Product

The sanitary tissue products of the present invention may exhibit a wet burst strength of greater than 420 g and/or greater than 430 g and/or greater than 440 g and/or greater than 450 g and/or greater than 460 g to about 2000 g and/or to about 1500 g and/or to about 1000 g and/or to about 900 g and/or to about 800 g.

The sanitary tissue products of the present invention may exhibit an initial total wet tensile of greater than 58 g/in and/or greater than 60 g/in and/or greater than 62 g/in and/or greater than 64 g/in and/or greater than 66 g/in to about 500 g/in and/or to about 450 g/in and/or to about 400 g/in and/or to about 300 g/in and/or to about 200 g/in and/or to about 100 g/in.

Method for Making Fibrous Structure

The fibrous structures of the present invention may be made by any suitable method known in the art so long as one or more non-naturally occurring hardwood pulp fibers that exhibit a handsheet tensile strength less than the handsheet tensile strength of the non-naturally occurring hardwood pulp fiber in its naturally occurring state as measured according to the Handsheet Tensile Strength Test Method described herein are used to make the fibrous structure. In one example, a method for making a fibrous structure according to the present invention comprises the steps of:

-   -   a. providing a fibrous composition comprising a non-naturally         occurring hardwood pulp fiber that exhibits a handsheet tensile         strength less than the handsheet tensile strength of the         non-naturally occurring hardwood pulp fiber in its naturally         occurring state as measured according to the Handsheet Tensile         Strength Test Method described herein; and     -   b. depositing the fibrous composition onto a collection device,         such as a fabric and/or a belt, to form a fibrous structure.

The method may further comprise one or more of the following steps: creping, compressively dewatering, and through-air-drying the fibrous structure.

The fibrous composition may comprise any suitable level of non-naturally occurring hardwood pulp fibers, such as enzyme treated hardwood pulp fibers.

Method for Making Sanitary Tissue Product

The sanitary tissue product of the present invention may be made by any suitable method known in the art so long as one or more fibrous structures of the present invention are used to make the sanitary tissue product.

Test Methods

Unless otherwise indicated, all tests described herein including those described under the Definitions section and the following test methods are conducted on samples, fibrous structure samples and/or sanitary tissue product samples and/or handsheets that have been conditioned in a conditioned room at a temperature of 73° F.±4° F. (about 23° C.±2.2° C.) and a relative humidity of 50%±10% for 2 hours prior to the test. Further, all tests are conducted in such conditioned room. Tested samples and felts and any equipment or materials should be subjected to 73° F.±4° F. (about 23° C.±2.2° C.) and a relative humidity of 50%±10% for 2 hours prior to testing.

Sample Preparation

To run the tests described below, handsheets must be prepared. The handsheets are prepared as follows.

The handsheets are low density handsheets and are prepared essentially according to TAPPI Standard T205 with the following modifications which are believed to more accurately reflect the sanitary tissue product manufacturing process.

For the handsheets, a fibrous slurry comprising tap water (with no pH adjustment) and pulp fibers is used.

An embryonic web is formed by depositing the fibrous slurry into a 12 inch×12 inch handsheet making apparatus on a monofilament polyester wire supplied by Appleton Wire Co. of Appleton Wis. The monofilament polyester wire has the following specifications: dimensions of 13.5 inch×13.5 inch; machine direction warp count of 84±1.5 fibers/inch; cross direction warp count of 76±3 fibers/inch; warp size/type of 0.17 mm/9FU; shute size/type of 0.17 mm/WP-110; caliper of 0.016±0.0005 inch; and air permeability of 720±25 cubic feet/minute.

The embryonic web is then transferred by vacuum from the monofilament polyester wire to a monofilament polyester papermaking fabric supplied by Appleton Wire Co. of Appleton, Wis. and dewatered by vacuum suction instead of pressing. The monofilament polyester papermaking fabric has the following specifications: dimensions 16 inch×14 inch; machine direction warp count of 36±1 fibers/inch; cross direction warp count of 30±3 fibers/inch; warp size/type of 0.40 mm/WP-87-12A-W; shute size/type of 0.40 mm/WP-801-12A-W; caliper of 0.027±0.001 inch; and air permeability of 397±25 cubic feet/minute.

The embryonic web and monofilament polyester wire are placed on top of monofilament polyester papermaking fabric such that the embryonic web contacts the papermaking fabric (a trilayer configuration of wire/web/fabric with fabric side down) is formed. The trilayer configuration is then passed lengthwise across a 13 inch× 1/16 inch wide vacuum slot box with a 90° flare set at a peak gauge reading of approximately 4.0 inches of Hg vacuum. The rate of the trilayer configuration passing across the vacuum slot should be uniform at a velocity of 16±5 inches/second. The vacuum is then increased to achieve a peak gauge reading of approximately 9.0 inches of Hg vacuum and the trilayer configuration is passed lengthwise across the same vacuum slot at the same rate of 16±5 inches/second 2 more times to form a handsheet. Note that the peak gauge reading is the amount of vacuum measured as the trilayer configuration passes across the vacuum slot.

The monofilament polyester wire is then carefully removed from the handsheet ensuring that no pulp fibers stick to the wire. The handsheet is then dried on a rotary drum dryer with a drying felt by passing the handsheet and the papermaking fabric between the drying felt and rotary drum dryer surface with the papermaking fabric against the rotary drum dryer surface and again with a second pass of the handsheet against the rotary drum dryer surface. The rotary drum dryer surface specifications are as follows: stainless steel polished finish cylinder with internal steam heating, horizontally mounted; 17 inches in length and 13 inches in diameter; 230±5° F.; rotation speed of 0.90±0.05 revolutions/minute; dryer felt is endless, 80 inches circumference by 16 inches wide, No. 11614, style X225, all wool from Noble Wood Lab Machine Company, Hoosick Falls, N.Y.; dryer felt tension as low and even as possible without slippage occurring between the dryer felt and the rotary drum dryer surface and uniform tracking.

The dried handsheet is 12 inch×12 inch with a resulting target basis weight of 16.5±1 lb/3,000 ft² and a target density of 0.15±0.06 g/cm³, unless otherwise noted.

The dried handsheet is then conditioned as described above before conducting any tests on the handsheets.

It will be recognized that the test methods described in this section require the making of handsheets following the specific procedure described above. Where a given product is in a form that includes chemical additives or where the fibrous structure is subjected to mechanical manipulation in generating the product, it is to be recognized that the determination of whether that product is within the scope of the present invention is made by forming handsheets in accordance with the present description, and measuring the physical properties of those handsheets, not measuring the physical properties of the product itself. That is, the fibers used to construct the product are used to make the handsheets as described; no application of additives or mechanical manipulation, aside from that discussed above, should occur.

From one handsheet, carefully cut four 1 in. wide strips of sample 6.0±0.1 inches in length in the “MD” direction. From a second handsheet of the same sample set, carefully cut four 1 in. wide strips of sample 6.0±0.1 inches in length in the “CD” direction. It is important that the cut be exactly perpendicular to the long dimension of the strip. The strip should also be free of wrinkles or excessive mechanical manipulation which can impact flexibility. Mark the direction very lightly on one end, keeping the same surface of the sample up for all strips. Later, the strips will be turned over for testing, thus it is important that one surface of the strip be clearly identified, however, it makes no difference which surface of the sample is designated as the upper surface.

Handsheet Tensile Strength Test Method

The Handsheet Tensile Strength Test is performed according to TAPPI Standards T220 om-88 and T494 om-88 on 1 inch×6 inch (about 2.5 cm×15.2 cm) strips of handsheets prepared as described above. An electronic tensile tester (Intellect II-STD, Thwing Albert Corp., Philadelphia, Pa.) is used and operated at a crosshead speed of 4 inches/minute (about 10 cm/minute) and a starting gauge length of 4 inches (about 10 cm). A minimum of n=8 tests are performed on each handsheet sample (4 machine direction strips and 4 cross direction strips). The resulting tensile strength values are recorded in g/in. and are divided by the average basis weight of the handsheet sample. The handsheet tensile strength for purpose of the present invention is the average of the basis weight normalized tensile strength values.

PFR Test Method

PFR (pulp filtration resistance) is measured using the following procedure. A sample of 2543 mL of a fiber suspension, having 0.1% consistency, prepared in a 19 liters tank, through a registry coupled to the bottom of a proportionate tank, returning it to the tank through the top portion. Repeat the procedure (note that the PFR must be carried out after taking 2543 mL for checking the consistency since the height of the water column inside the proportionate tank changes the measure value). Measure the suspension temperature. Record the value in Celsius degrees. Install the connection for PFR measuring in the inferior registry of the proportionate tank of sample; Put the 100 mL glass flask below the connection (note that since it refers to a dynamic measurement having a specific recipient to this end, there is no need to calibrate it). With a single and fast movement, open the valve for sample collection and at the same time activate the chronometer in order to measure the time, in seconds, required for filling the 100 mL, flask up to its mark. Record the time “A”, in seconds. Discard the filtrate and without washing the screen of the connection, measure the time needed for filling the flask again. Record the time “B” in seconds. Repeat the previous item, recording the time “C” in seconds. Remove the connection and wash it in counter flow so as to remove all the pulp retained, checking that the connection sieve is clean and free of fibers which may dry and change further tests. Calculate the PFR value as follows:

PFR=√{square root over (E×(B+C−2A)/1,5)}

wherein:

-   -   A, B and C=time measurements in seconds.     -   E=1+0.013 (T-75)     -   T=temperature in Fahrenheit degrees.         A short formula may be used:

PFR=Kx√{square root over (B+C−2A)}

wherein:

K=√{square root over (E/1,5)}

then:

K=√{square root over ([1+0,013(T−75)])}

“K” values to temperatures ranging from 70° F. (21° C.) and 77° F. (25° C.).

° C. ° F. “K” factor 21.0 69.8 0.7884 21.5 70.7 0.7933 22.0 71.6 0.7982 22.5 72.5 0.8031 23.0 73.4 0.8080 23.5 74.3 0.8128 24.0 75.2 0.8176 24.5 76.1 0.8223 25.0 77.0 0.8270

The pulp filtration resistance (PFR) can be obtained by measuring the Canadian Standard Freeness (CSF) according to TAPPI Standard T-227 om-09. CSF is related to PFR by the following equation: PFR=78918*CSF^(−1.4688).

Wet Burst Strength Test Method

Wet burst strength may be measured using a Thwing-Albert Burst Tester Cat. No. 177 equipped with a 2000 g load cell commercially available from Thwing-Albert Instrument Company, Philadelphia, Pa.

Wet burst strength is measured by taking two sanitary tissue product samples. Using scissors, cut the samples in half in the MD so that they are approximately 228 mm in the machine direction and approximately 114 mm in the cross machine direction, each two (2) plies thick (you now have 4 samples). First, condition the samples for two (2) hours at a temperature of 73° F.±2° F. (about 23° C.±1° C.) and a relative humidity of 50%±2%. Next age the samples by stacking the samples together with a small paper clip and “fan” the other end of the stack of samples by a clamp in a 105° C. (±1° C.) forced draft oven for 5 minutes (±10 seconds). After the heating period, remove the sample stack from the oven and cool for a minimum of three (3) minutes before testing. Take one sample strip, holding the sample by the narrow cross machine direction edges, dipping the center of the sample into a pan filled with about 25 mm of distilled water. Leave the sample in the water four (4) (±0.5) seconds. Remove and drain for three (3) (±0.5) seconds holding the sample so the water runs off in the cross machine direction. Proceed with the test immediately after the drain step. Place the wet sample on the lower ring of a sample holding device of the Burst Tester with the outer surface of the sample facing up so that the wet part of the sample completely covers the open surface of the sample holding ring. If wrinkles are present, discard the samples and repeat with a new sample. After the sample is properly in place on the lower sample holding ring, turn the switch that lowers the upper ring on the Burst Tester. The sample to be tested is now securely gripped in the sample holding unit. Start the burst test immediately at this point by pressing the start button on the Burst Tester. A plunger will begin to rise toward the wet surface of the sample. At the point when the sample tears or ruptures, report the maximum reading. The plunger will automatically reverse and return to its original starting position. Repeat this procedure on three (3) more samples for a total of four (4) tests, i.e., four (4) replicates. Report the results as an average of the four (4) replicates, to the nearest g.

Initial Total Wet Tensile Test Method

The initial total wet tensile of sanitary tissue products of the present invention is determined using a Thwing-Albert EJA Material Tester Instrument, Cat. No. 1350, equipped with 5000 g load cell available from Thwing-Albert Instrument Company, 14 Collings Ave. W. Berlin, N.J. 08091.10% of the 5000 g load cell is utilized for the wet tensile test.

i. Sample Preparation—A strip of sample to be tested [2.54 cm (1 inch) wide by greater than 5.08 cm (2 inches)] long is obtained.

ii. Operation—The test settings for the instrument are:

Crosshead speed—10.16 cm/minute (4.0 in/minute) Initial gauge length—2.54 cm (1.0 inch)

Adjust the load cell to read zero plus or minus 0.5 grams_(force).

iii. Testing Samples—One end of the sample strip is placed between the upper jaws of the machine and clamped. After verifying that the sample strip is hanging straight between the lower jaws, clamp the other end of the sample strip in the lower jaws.

a. Pre-Test—Strain the sample strip to 25 grams_(force) (+/−10 grams_(force)) at a strain rate of 3.38 cm/minute (1.33 in/minute) prior to wetting the sample strip. The distance between the upper and lower jaws now being greater than 2.54 cm (1.0 inch). This distance now becomes the new zero-strain position for the forthcoming wet test.

b. Wet Test—While the sample strip is still at 25 grams_(force) (+/−10 grams_(force)), it is wetted, starting near the upper jaws, a water/0.1% Pegosperse® ML200 (available from Lonza Inc. of Allendale, N.J.) solution [having a temperature of about 73° F.±4° F. (about 23° C.±2.2° C.)] is delivered to the sample strip via a 2 ml disposable pipet. Do not contact the sample strip with the pipet and do not damage the sample strip by using excessive squirting pressure. The solution is continuously added until the sample strip is visually determined to be completely saturated between the upper and lower jaws. At this point, the load cell is re-adjusted to read zero plus or minus 0.5 grams_(force).

The sample strip is then strained at a rate of 10.16 cm/minute (4 inches/minute) and continues until the sample strip is strained past its failure point (failure point being defined as the point on the force-strain curve where the sample strip falls to 50% of its peak strength after it has been strained past its peak strength). The straining of the sample strip is initiated between 5-10 seconds after the sample is initially wetted. The initial result of the test is an array of data points in the form of load (grams_(force)) versus strain (where strain is calculated as the crosshead displacement (cm of jaw movement from starting point) divided by the initial separation distance (cm) between the upper and lower jaws after the pre-test.

The sample is tested in two orientations, referred to here as MD (machine direction, i.e., in the same direction as the continuously wound reel and forming fabric) and CD (cross-machine direction, i.e., 90° from MD). The MD and CD wet tensile strengths are determined using the above equipment and calculations in the following manner:

ITWT(g _(f)/inch)=Peak Load_(MD)(g _(f))/1(inch_(width))+Peak Load_(CD)(g _(f))/1(inch_(width))

Non-limiting Examples Example 1 Multi-ply Sanitary Tissue Product Using Non-Enzyme Treated Hardwood Pulp Fibers (Control)

A pilot scale Fourdrinier papermaking machine is used in the present example. A 3% by weight aqueous slurry of Northern Softwood Kraft (NSK) (50/50 mixture of softwood pulp marketed by Abitibi Bowater Incorporated of Montreal, PQ, Canada and by Zellstof Celgar, Mercer International from Castlegar, BC, Canada mill) is made up in a conventional re-pulper. The NSK slurry is refined gently and a 3% solution of a permanent wet strength resin (i.e. Kymene 1142 marketed by Hercules Incorporated of Wilmington, Del.) is added to the NSK stock pipe at a rate of 1% by weight of the dry fibers. The adsorption of Kymene 1142 to NSK is enhanced by an in-line mixer. A 1% solution of Carboxy Methyl Cellulose (CMC) (i.e. FinnFix from CP Kelco U.S., Inc. of Atlanta, Ga.) is added after the in-line mixer at a rate of 0.35% by weight of the dry fibers to enhance the dry strength of the fibrous substrate. A 3% by weight aqueous slurry Eucalyptus fibers (from Fibria's Aracruz, Brazil mill) is made up in a conventional re-pulper. A 1% solution of defoamer (i.e. Advantage DF285 marketed by Hercules Incorporated of Wilmington, Del.) is added to eucalyptus line before the in-line mixer at a rate of 0.05% by weight of the dry fibers.

The NSK furnish and the Eucalyptus fibers are fed to the head box and deposited onto a Fourdrinier wire as a homogenous mixture to form an embryonic web. Dewatering occurs through the Foudrinier wire and is assisted by a deflector and vacuum boxes. The Fourdrinier wire is of a 5-shed, satin weave configuration having 84 machine-direction and 76 cross-machine-direction monofilaments per inch, respectively. The embryonic wet web is transferred from the Fourdrinier wire, at a fiber consistency of about 19% at the point of transfer, to a photo-polymer fabric having 150 SP cells per square inch, 25 percent knuckle areas and 18.5 mils of photo-polymer depth. Further de-watering is accomplished by vacuum assisted drainage until the web has a fiber consistency of about 23%. The patterned web is pre-dried by air blow-through to a fiber consistency of about 60% by weight. The web is then adhered to the surface of a Yankee dryer with a sprayed creping adhesive comprising aqueous solution of Polyvinyl Alcohol (PVA) (i.e. Vinylon 88-44 marketed by Wego Chemical and mineral corporation of Great Neck, N.Y.) at a rate of 0.1% by weight and a crepe aid (i.e. Unicrepe 457T20 marketed by Georgia Pacific Chemicals LLC of Atlanta, Ga.) at a rate of 0.025% by weight of the dry fibers. The fiber consistency is increased to an estimated 96% before the dry creping the web with a doctor blade. The doctor blade has a bevel angle of about 25 degrees and is positioned with respect to the Yankee dryer to provide an impact angle of about 81 degrees; the Yankee dryer is operated at about 800 fpm (feet per minute) (about 244 meters per minute). The dry web is formed into roll at a speed of 760 fpm (232 meters per minutes).

Two plies of the web are formed into a 2-ply paper towel by embossing and laminating them together using PVA adhesive. The 2-ply paper towel has about 47 g/m² basis weight and contains 65% by weight Northern Softwood Kraft and 35% by weight Eucalyptus furnish. The 2-ply towel exhibits a wet burst strength of about 418 g, total dry tensile of about 2297 g/in and wet burst strength to total dry tensile ratio of 0.18.

Example 2 Multi-ply Sanitary Tissue Product Using Enzyme Treated Hardwood Pulp Fibers (Invention)

A paper towel is made by a method similar to that of Example 1, but replacing the Eucalyptus fibers with enzyme treated Eucalyptus pulp fibers from Fibria, Brazil. The Eucalyptus pulp fibers are treated by Fibria as follows. A xylanase enzymatic treatment stage is carried out using a xylanase charge of 1 kilogram of xylanase/ton of cellulose, pH of about 7, temperature of 75° C., in a 3 hour treatment, using a suspension at 11% consistency. An acid step is then performed at 90° C., pH of about 3 to 4.5 using sulfuric or hydrochloric acid to set the pH, for 3 hours and 11% consistency.

After the enzymatic treatment, a method to denature the enzyme was conducted, which consisted of washing the treated cellulose, dewatering until a consistency of 25 to 30% by weight is achieved, and heating of the medium to 85 to 95° C. for 10 to 15 minutes.

The xylanase can be obtained from Novozymes A/S of Bagsvxrd, Denmark. The xylanase is used at a rate of 0.1% by weight of dry pulp fibers during the bleaching sequence having an acid step.

The 2-ply paper towel made has about 47 g/m² basis weight and contains 65% by weight Northern Softwood Kraft and 35% by weight xylanase treated Eucalyptus. The 2-ply towel exhibits a wet burst strength of about 465 g, total dry tensile of about 2337 g/in and wet burst strength to total dry tensile ratio of 0.20.

Example 3 Multi-ply Sanitary Tissue Product Using Enzyme Treated Hardwood Pulp Fibers (Invention)

A paper towel is made by a method similar to that of Example 1, but replacing the Eucalyptus fiber with enzyme treated Eucalyptus pulp fibers from Fibria, Brazil. The Eucalyptus pulp fibers are treated by Fibria as follows. A first enzymatic treatment stage is carried out using a xylanase charge of 0.5 kilogram of xylanase/ton of cellulose, pH of about 7, temperature of 75° C., in a 3 hour treatment, using a suspension at 11% consistency. A second enzyme treatment stage is performed using a cellulase charge of 1 kilogram of cellulase/ton of cellulose, pH of about 7. The acid step is performed at 90° C., pH of about 3 to 4.5 using sulfuric or hydrochloric acid to set the pH, for 3 hours and 11% consistency.

After the enzymatic treatment, a method to denature the enzyme was conducted, which consisted of washing the treated cellulose, dewatering until a consistency of 25 to 30% by weight is achieved, and heating of the medium to 85 to 95° C. for 10 to 15 minutes.

The xylanase and cellulase can be obtained from Novozymes A/S of Bagsvxrd, Denmark. The xylanase is used at a rate of 0.05% by weight of dry pulp fibers and the cellulase is used at a rate of 0.1% by weight of dry pulp fibers during the bleaching sequence having an acid step.

The 2-ply paper towel has about 47 g/m² basis weight and contains 65% by weight Northern Softwood Kraft and 35% by weight xylanase and cellulase treated Eucalyptus. The 2-ply towel exhibits a wet burst strength of about 464 g, total dry tensile of about 2331 g/in and wet burst strength to total dry tensile ratio of 0.20.

Example 4 Multi-ply Sanitary Tissue Product Using Non-Enzyme Treated Hardwood Pulp Fibers (Control)

A pilot scale Fourdrinier papermaking machine is used in the present example. A 3% by weight aqueous slurry of Northern Softwood Kraft (NSK) (marketed by Weyerhaeuser Co. Federal Way, Wash.) is made up in a conventional re-pulper. The NSK slurry is passed through a refiner at no load and a 1% solution of a aldehyde functionalized cationic polyacrylamide temporary wet strength resin (i.e. PAREZ 750C marketed by Kemira Chemicals, Inc. of Kennesaw, Ga.) is added to the NSK stock pipe at a rate of 0.125% by weight of the dry fibers. A 3% by weight aqueous slurry Eucalyptus fibers (from Fibria's Aracruz, Brazil mill) is made up in a conventional re-pulper. A 1% solution of a aldehyde functionalized cationic polyacrylamide temporary wet strength resin (i.e. PAREZ 750C marketed by Kemira Chemicals, Inc. of Kennesaw, Ga.) is added to the Eucalyptus stock pipe at a rate of 0.025% by weight of the dry fibers.

The NSK furnish and the Eucalyptus fibers are layered in the head box and deposited onto a Fourdrinier wire as different layers to form an embryonic web. Dewatering occurs through the Foudrinier wire and is assisted by a deflector and vacuum boxes. The Fourdrinier wire is of a 5-shed, satin weave configuration having 84 machine-direction and 76 cross-machine-direction monofilaments per inch, respectively. The embryonic wet web is transferred from the Fourdrinier wire, at a fiber consistency of about 19% at the point of transfer, to a photo-polymer fabric having 20 Structured Linearly Aligned Molding cells per square inch, 40 percent knuckle areas and 11.6 mils of photo-polymer depth. Further de-watering is accomplished by vacuum assisted drainage until the web has a fiber consistency of about 26%. The patterned web is pre-dried by air blow-through to a fiber consistency of about 54% by weight. The web is then adhered to the surface of a Yankee dryer with a sprayed creping adhesive comprising aqueous solution of Polyvinyl Alcohol (PVA) (i.e. Vinylon 88-44 marketed by Wego Chemical and mineral corporation of Great Neck, N.Y.) at a rate of 0.1% by weight and a crepe aid (i.e. Unicrepe 457T20 marketed by Georgia Pacific Chemicals LLC of Atlanta, Ga.) at a rate of 0.025% by weight of the dry fibers. The fiber consistency is increased to an estimated 96% before the dry creping the web with a doctor blade. The doctor blade has a bevel angle of about 25 degrees and is positioned with respect to the Yankee dryer to provide an impact angle of about 81 degrees; the Yankee dryer is operated at about 800 fpm (feet per minute) (about 244 meters per minute). The dry web is formed into roll at a speed of 672 fpm (205 meters per minutes).

Two plies of the web are formed into toilet paper products by laminating them together using a hot melt adhesive (i.e. Cycloflex 34-121C marketed by Henkel Corporation of Bridgewater, N.J.). A cationic quad based surfactant at a rate of 0.375% by weight of the dry fibers also applied to the product. The 2-ply toilet paper has about 50.4 g/m² basis weight and contains 35% by weight Northern Softwood Kraft and 65% by weight Eucalyptus furnish. The 2-ply toilet paper exhibits an initial total wet tensile of about 56.6 g/in, total dry tensile of about 475.6 g/in and initial total wet tensile to total dry tensile ratio of 0.119.

Example 5 Multi-ply Sanitary Tissue Product Using Enzyme Treated Hardwood Pulp Fibers (Invention)

A toilet paper is made by a method similar to that of Example 4, but replacing the Eucalyptus fiber with enzyme treated Eucalyptus pulp fibers from Fibria, Brazil. The Eucalyptus pulp fibers are treated by Fibria as follows. A xylanase enzymatic treatment stage is carried out using a xylanase charge of 1 kilogram of xylanase/ton of cellulose, pH of about 7, temperature of 75° C., in a 3 hour treatment, using a suspension at 11% consistency. An acid step is then performed at 90° C., pH of about 3 to 4.5 using sulfuric or hydrochloric acid to set the pH, for 3 hours and 11% consistency.

After the enzymatic treatment, a method to denature the enzyme was conducted, which consisted of washing the treated cellulose, dewatering until a consistency of 25 to 30% by weight is achieved, and heating of the medium to 85 to 95° C. for 10 to 15 minutes.

The xylanase can be obtained from Novozymes A/S of Bagsvard, Denmark. The xylanase is used at a rate of 0.1% by weight of dry pulp fibers during the bleaching sequence having an acid step.

The 2-ply toilet paper has about 50.4 g/m² basis weight and contains 35% by weight Northern Softwood Kraft and 65% by weight xylanase treated Eucalyptus. The 2-ply toilet paper exhibits an initial total wet tensile of about 62.6 g/in, total dry tensile of about 475.4 m/in and initial total wet tensile to total dry tensile ratio of 0.132.

Example 6 Multi-ply Sanitary Tissue Product Using Enzyme Treated Hardwood Pulp Fibers (Invention)

A toilet paper is made by a method similar to that of Example 4, but replacing the Eucalyptus fiber with enzyme treated Eucalyptus pulp fibers from Fibria, Brazil. The Eucalyptus pulp fibers are treated by Fibria as follows. A first enzymatic treatment stage is carried out using a xylanase charge of 0.5 kilogram of xylanase/ton of cellulose, pH of about 7, temperature of 75° C., in a 3 hour treatment, using a suspension at 11% consistency. A second enzyme treatment stage is performed using a cellulase charge of 1 kilogram of cellulase/ton of cellulose, pH of about 7. The acid step is performed at 90° C., pH of about 3 to 4.5 using sulfuric or hydrochloric acid to set the pH, for 3 hours and 11% consistency.

After the enzymatic treatment, a method to denature the enzyme was conducted, which consisted of washing the treated cellulose, dewatering until a consistency of 25 to 30% by weight is achieved, and heating of the medium to 85 to 95° C. for 10 to 15 minutes.

The xylanase and cellulase can be obtained from Novozymes A/S of Bagsvxrd, Denmark. The xylanase is used at a rate of 0.05% by weight of dry pulp fibers and the cellulase is used at a rate of 0.1% by weight of dry pulp fibers during the bleaching sequence having an acid step.

The 2-ply toilet paper has about 50.4 g/m² basis weight and contains 35% by weight Northern Softwood Kraft and 65% by weight xylanase and cellulase treated Eucalyptus. The 2-ply toilet paper exhibits an initial total wet tensile of about 65.8 g/in, total dry tensile of about 519.6 g/in and initial total wet tensile to total dry tensile ratio of 0.127.

Example 7 Multi-ply Sanitary Tissue Product Using Enzyme Treated Hardwood Pulp Fibers (Invention)

A toilet paper is made by a method similar to that of Example 4, but replacing the Eucalyptus fiber with enzyme treated Eucalyptus pulp fibers from Fibria, Brazil. The Eucalyptus pulp fibers are treated by Fibria as follows. A xylanase enzymatic treatment stage is carried out using a xylanase charge of 0.5 kilogram of xylanase/ton of cellulose, pH of about 7, temperature of 75° C., in a 3 hour treatment, using a suspension at 11% consistency. An acid step is then performed at 90° C., pH of about 3 to 4.5 using sulfuric or hydrochloric acid to set the pH, for 3 hours and 11% consistency.

After the enzymatic treatment, a method to denature the enzyme was conducted, which consisted of washing the treated cellulose, dewatering until a consistency of 25 to 30% by weight is achieved, and heating of the medium to 85 to 95° C. for 10 to 15 minutes.

The xylanase can be obtained from Verenium Corporation of San Diego, Calif. The xylanase is used at a rate of 0.05% by weight of dry pulp fibers during the bleaching sequence having an acid step.

The 2-ply toilet paper has about 50.4 g/m² basis weight and contains 35% by weight Northern Softwood Kraft and 65% by weight xylanase treated Eucalyptus. The 2-ply toilet paper exhibits an initial total wet tensile of about 68.4 g/in, total dry tensile of about 505 g/in and initial total wet tensile to total dry tensile ratio of 0.135.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”

Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. 

1. A fibrous structure comprising a non-naturally occurring hardwood pulp fiber that exhibits a handsheet tensile strength as measured according to the Handsheet Tensile Strength Test Method described herein less than the handsheet tensile strength of the non-naturally occurring hardwood pulp fiber in its naturally occurring state.
 2. The fibrous structure according to claim 1 wherein the non-naturally occurring hardwood pulp fiber is obtained from a naturally occurring hardwood pulp fiber.
 3. The fibrous structure according to claim 2 wherein the naturally occurring hardwood pulp fiber is obtained from a fiber source selected from the group consisting of: Acacia, Eucalyptus, Maple, Oak, Aspen, Birch, Cottonwood, Alder, Ash, Cherry, Elm, Hickory, Poplar, Gum, Walnut, Locust, Sycamore, Beech, Catalpa, Sassafras, Gmelina, Albizia, Anthocephalus, Magnolia, and mixtures thereof.
 4. The fibrous structure according to claim 2 wherein the naturally occurring hardwood pulp fiber is obtained from Eucalyptus.
 5. The fibrous structure according to claim 2 wherein the naturally occurring hardwood pulp fiber comprises a tropical hardwood pulp fiber.
 6. The fibrous structure according to claim 1 wherein the non-naturally occurring hardwood pulp fiber is obtained by enzymatically treating a naturally occurring hardwood pulp fiber.
 7. The fibrous structure according to claim 6 wherein the non-naturally occurring hardwood pulp fiber is obtained by treating a naturally occurring hardwood pulp fiber with xylanase.
 8. The fibrous structure according to claim 6 wherein the non-naturally occurring hardwood pulp fiber is obtained by treating a naturally occurring hardwood pulp fiber with an enzyme composition comprising xylanase and cellulase.
 9. The fibrous structure according to claim 1 wherein the non-naturally occurring hardwood pulp fiber exhibits a PFR of 7.4 or less.
 10. A single- or multi-ply sanitary tissue product comprising one or more fibrous structures according to claim
 1. 11. A sanitary tissue product comprising a non-naturally occurring hardwood pulp fiber that exhibits a handsheet tensile strength as measured according to the Handsheet Tensile Strength Test Method described herein less than the handsheet tensile strength of the non-naturally occurring hardwood pulp fiber in its naturally occurring state, wherein the sanitary tissue product exhibits a greater wet burst strength as measured according to the Wet Burst Strength Test Method described herein and/or a greater initial total wet tensile as measured by the Initial Total Wet Tensile Test Method described herein than a sanitary tissue product that comprises the non-naturally occurring hardwood pulp fiber in its naturally occurring state.
 12. The sanitary tissue product according to claim 11 wherein the non-naturally occurring hardwood pulp fiber is obtained from a naturally occurring hardwood pulp fiber.
 13. The sanitary tissue product according to claim 12 wherein the naturally occurring hardwood pulp fiber is obtained from a fiber source selected from the group consisting of: Acacia, Eucalyptus, Maple, Oak, Aspen, Birch, Cottonwood, Alder, Ash, Cherry, Elm, Hickory, Poplar, Gum, Walnut, Locust, Sycamore, Beech, Catalpa, Sassafras, Gmelina, Albizia, Anthocephalus, Magnolia, and mixtures thereof.
 14. The sanitary tissue product according to claim 12 wherein the naturally occurring hardwood pulp fiber is obtained from Eucalyptus.
 15. The sanitary tissue product according to claim 12 wherein the naturally occurring hardwood pulp fiber comprises a tropical hardwood pulp fiber.
 16. The sanitary tissue product according to claim 11 wherein the non-naturally occurring hardwood pulp fiber is obtained by enzymatically treating a naturally occurring hardwood pulp fiber.
 17. The sanitary tissue product according to claim 16 wherein the non-naturally occurring hardwood pulp fiber is obtained by treating a naturally occurring hardwood pulp fiber with xylanase.
 18. The sanitary tissue product according to claim 16 wherein the non-naturally occurring hardwood pulp fiber is obtained by treating a naturally occurring hardwood pulp fiber with an enzyme composition comprising xylanase and cellulase.
 19. The sanitary tissue product according to claim 11 wherein the non-naturally occurring hardwood pulp fiber exhibits a PFR of 7.4 or less.
 20. A method for making a fibrous structure comprising the steps of: a. providing a fibrous composition comprising a non-naturally occurring hardwood pulp fiber that exhibits a handsheet tensile strength as measured according to the Handsheet Tensile Strength Test Method described herein less than the handsheet tensile strength of the non-naturally occurring hardwood pulp fiber in its naturally occurring state; and b. depositing the fibrous composition onto a collection device to form a fibrous structure. 